User equipment having multiple subscriber identity modules with improved suspend / resume operation

ABSTRACT

Devices and associated methods for operating a dual-subscriber identity module (SIM) dual-standby (DSDS) user equipment device (UE) configured with a first SIM and a second SIM. The UE performs communications with a first cellular network using the first SIM and a first radio resource control (RRC) connection, and receives a request to perform a higher priority communication using the second SIM. In response to the request to perform the higher priority communication, the UE transmits a request to the first network to suspend the first RRC connection. After transmission of the request to suspend the first RRC connection, the UE receives a message from the first network to place the first RRC connection in an inactive state, and initiates a timer, wherein the timer is used to determine whether the first RRC connection remains in the inactive state or transitions to an idle state.

PRIORITY CLAIMS

This application claims benefit of priority to Chinese Application No.201910618956.0, titled “UE Having Multiple Subscriber Identity Moduleswith Improved Suspend/Resume Operation”, filed Jul. 10, 2019, which ishereby incorporated by reference in its entirety as though fully andcompletely set forth herein.

FIELD

The present disclosure relates to the field of wireless communication,and more particularly to a user equipment (UE) having multiplesubscriber identity modules which performs improved network notificationduring SIM suspend/resume operations.

DESCRIPTION OF THE RELATED ART

Wireless communication systems are rapidly growing in usage. Further,wireless communication technology has evolved from voice-onlycommunications to also include the transmission of data, such asInternet and multimedia content. In order to enable a wireless device toaccess a wireless communication network (e.g., a cellulartelecommunication network) according to at least some wirelesscommunication technologies and standards, a user may subscribe to aservice provider (a “carrier”), who in turn may provide such services tothe user, e.g., via a wireless communication network which they operate.Such subscribers in a wireless communication network are typicallyassigned subscriber identity information, which may for example bestored as part of a subscriber identity module (SIM) in the subscriber'swireless device. For example, many wireless devices may be provided witha slot for a removable subscriber identity module (SIM) card. Providingsuch a slot may enable users to select and/or change their subscriberidentity independently from the wireless device, as the user may be ableto switch out their current SIM card for a different SIM card at anygiven time as desired. More recently, UE devices may come equipped withan electronic SIM (eSIM), wherein an embedded memory in the UE storessubscriber identity information for the user.

Many UE devices today are being designed as dual SIM or multi SIMphones, wherein the UE is capable of storing two or more sets ofsubscriber identity information for the user. This enables the UE to,for example, store first subscriber identity information for a user'shome telephone number and also store second subscriber identityinformation for the user's business telephone number. Alternatively, orin addition, one of the SIMs can be used primarily for voice calls withthe other one can be used primarily for data transfers. Dual SIM ormulti SIM UE devices have been especially popular in more recentlydeveloping economies such as China.

One type of dual SIM UE is referred to as Dual SIM Dual Active (DSDA)and may contain multiple receiver (Rx) architectures. A DSDA UE iscapable of using two SIMs and two radios, so as to maintain two activesets of data communication simultaneously, e.g., the UE may beconducting a voice call using one SIM while performing datacommunication (e.g., Internet browsing) on the second SIM.

Another type of dual SIM UE may have only a single Rx architecture(e.g., for cost savings and reduced size requirements) and may bereferred to as Dual SIM Dual Standby (DSDS). In a UE which contains onlya single receiver, only one SIM may be in operation at any given time.Thus when the UE is utilizing a first SIM for a voice call, the secondSIM will be idle. In some instances, when a SIM is currently in use andthe UE detects initiation of a higher priority activity which requiresthe other SIM, the UE may suspend activity on the first SIM in order toundertake the higher priority activity on the other SIM. In a UE havingmultiple SIM devices and only one radio, the UE may encounter networkproblems when a SIM suspends and then subsequently resumes a radioresource control (RRC) connection with the network

Accordingly, improvements in wireless communications, and in particularwith respect to multiple subscriber identity functionality, would bedesirable.

SUMMARY

In light of the foregoing and other concerns, it would be desirable toexpand the functionality of wireless devices with respect to subscriberidentities. In particular, it would be desirable to provide improvedstate synchronization between the wireless device and the network in anenergy-efficient manner. The present disclosure relates to suchtechniques for facilitating state synchronization according to variousembodiments.

Embodiments of the disclosure may thus be directed to methods for statesynchronization in a dual-SIM dual-standby (DSDS) UE device, to a UEdevice configured to implement such a method, and/or to a non-transitorycomputer accessible memory medium storing program instructionsexecutable by a processor to implement such a method. The UE device mayinclude a radio (e.g., including one or more antennas and/or other radiocomponents) for performing wireless communication. The UE device mayalso include a processing element configured to implement part or all ofthe method (e.g., by executing program instructions). The UE device mayfurther include one or more user interface elements, such as a display.In addition, the UE device may include a non-transitory computeraccessible memory medium, which may store program instructionsexecutable by the UE.

In some embodiments, a DSDS UE is configured with a first SIM and asecond SIM. The UE performs communications with a first cellular networkusing the first SIM and a first radio resource control (RRC) connection,and receives a request to perform a higher priority communication usingthe second SIM. In response to the request to perform the higherpriority communication, the UE transmits a request to the first networkto suspend the first RRC connection. After transmission of the requestto suspend the first RRC connection, the UE receives a message from thefirst network to place the first RRC connection in an inactive state,and initiates a timer, wherein the timer is used to determine whetherthe first RRC connection remains in the inactive state or transitions toan idle state.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present subject matter can be obtainedwhen the following detailed description of the preferred embodiment isconsidered in conjunction with the following drawings, in which:

FIGS. 1-2 illustrate exemplary wireless communication systems between UEdevices and one or more networks through one or more base stations,according to some embodiments;

FIG. 3 illustrates an example cellular network system including anevolved packet core (EPC), according to some embodiments;

FIG. 4 illustrates an example block diagram of a user equipment device;

FIG. 5 illustrates an example block diagram of a base station;

FIG. 6 is a message sequence chart illustrating an example method wherethe UE provides information to the network regarding suspend/resumeoperations to maintain RRC state synchronization, where resumptionoccurs without a timeout event, according to some embodiments;

FIG. 7 is a message sequence chart illustrating an example method wherethe UE provides information to the network regarding suspend/resumeoperations to maintain RRC state synchronization, where resumptionoccurs with a timeout event, according to some embodiments;

FIG. 8 is a message sequence chart illustrating an example method wherethe UE provides information to the network regarding suspend/resumeoperations and the network stores connected state information tomaintain RRC state synchronization, according to some embodiments;

FIG. 9 is a message sequence chart illustrating problems that arise dueto RRC state mismatch;

FIG. 10 is a message sequence chart illustrating an example method wherea suspension timer is utilized to avoid RRC state mismatch, according tosome embodiments;

FIG. 11 is a message sequence chart illustrating an example method wherenetwork coordination is utilized to avoid RRC state mismatch, accordingto some embodiments; and

FIG. 12 is a message sequence chart illustrating an example method wherea UE informs a network of connection release to avoid RRC statemismatch, according to some embodiments.

While the features described herein are susceptible to variousmodifications and alternative forms, specific embodiments thereof areshown by way of example in the drawings and are herein described indetail. It should be understood, however, that the drawings and detaileddescription thereto are not intended to be limiting to the particularform disclosed, but on the contrary, the intention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the subject matter as defined by the appended claims.

DETAILED DESCRIPTION OF THE EMBODIMENTS Acronyms

The following acronyms are used in this disclosure.

3GPP: Third Generation Partnership Project

3GPP2: Third Generation Partnership Project 2

GSM: Global System for Mobile Communications

UMTS: Universal Mobile Telecommunications System

LTE: Long Term Evolution

LTE-A: LTE-Advanced

SIM: Subscriber Identity Module

eSIM: Embedded SIM

IMSI: International Mobile Subscriber Identity

MCC: Mobile Country Code

MNC: Mobile Network Code

Terms

The following is a glossary of terms used in this disclosure:

Memory Medium—Any of various types of memory devices or storage devices.The term “memory medium” is intended to include an installation medium,e.g., a CD-ROM, floppy disks, or tape device; a computer system memoryor random access memory such as DRAM, DDR RAM, SRAM, EDO RAM, RambusRAM, etc.; a non-volatile memory such as a Flash, magnetic media, e.g.,a hard drive, or optical storage; registers, or other similar types ofmemory elements, etc. The memory medium may include other types ofmemory as well or combinations thereof. In addition, the memory mediummay be located in a first computer system in which the programs areexecuted, or may be located in a second different computer system whichconnects to the first computer system over a network, such as theInternet. In the latter instance, the second computer system may provideprogram instructions to the first computer for execution. The term“memory medium” may include two or more memory mediums which may residein different locations, e.g., in different computer systems that areconnected over a network. The memory medium may store programinstructions (e.g., embodied as computer programs) that may be executedby one or more processors.

Carrier Medium—a memory medium as described above, as well as a physicaltransmission medium, such as a bus, network, and/or other physicaltransmission medium that conveys signals such as electrical,electromagnetic, or digital signals.

Programmable Hardware Element—includes various hardware devicescomprising multiple programmable function blocks connected via aprogrammable interconnect. Examples include FPGAs (Field ProgrammableGate Arrays), PLDs (Programmable Logic Devices), FPOAs (FieldProgrammable Object Arrays), and CPLDs (Complex PLDs). The programmablefunction blocks may range from fine grained (combinatorial logic or lookup tables) to coarse grained (arithmetic logic units or processorcores). A programmable hardware element may also be referred to as“reconfigurable logic”.

Computer System—any of various types of computing or processing systems,including a personal computer system (PC), mainframe computer system,workstation, network appliance, Internet appliance, personal digitalassistant (PDA), personal communication device, smart phone, televisionsystem, grid computing system, or other device or combinations ofdevices. In general, the term “computer system” can be broadly definedto encompass any device (or combination of devices) having at least oneprocessor that executes instructions from a memory medium.

User Equipment (UE) (or “UE Device”)—any of various types of computersystems devices which are mobile or portable and which performs wirelesscommunications. Examples of UE devices include mobile telephones orsmart phones (e.g., iPhone™, Android™-based phones), wearable devices(e.g., smart watch, smart glasses), portable gaming devices (e.g.,Nintendo DS™, PlayStation Portable™ Gameboy Advance™, iPhone™), laptops,PDAs, portable Internet devices, music players, data storage devices, orother handheld devices, etc. In general, the term “UE” or “UE device”can be broadly defined to encompass any electronic, computing, and/ortelecommunications device (or combination of devices) which is easilytransported by a user and capable of wireless communication.

Base Station—The term “Base Station” has the full breadth of itsordinary meaning, and at least includes a wireless communication stationinstalled at a fixed location and used to communicate as part of awireless telephone system or radio system.

Processing Element—refers to various elements or combinations ofelements. Processing elements include, for example, circuits such as anASIC (Application Specific Integrated Circuit), portions or circuits ofindividual processor cores, entire processor cores, individualprocessors, programmable hardware devices such as a field programmablegate array (FPGA), and/or larger portions of systems that includemultiple processors.

Automatically—refers to an action or operation performed by a computersystem (e.g., software executed by the computer system) or device (e.g.,circuitry, programmable hardware elements, ASICs, etc.), without userinput directly specifying or performing the action or operation. Thusthe term “automatically” is in contrast to an operation being manuallyperformed or specified by the user, where the user provides input todirectly perform the operation. An automatic procedure may be initiatedby input provided by the user, but the subsequent actions that areperformed “automatically” are not specified by the user, i.e., are notperformed “manually”, where the user specifies each action to perform.For example, a user filling out an electronic form by selecting eachfield and providing input specifying information (e.g., by typinginformation, selecting check boxes, radio selections, etc.) is fillingout the form manually, even though the computer system must update theform in response to the user actions. The form may be automaticallyfilled out by the computer system where the computer system (e.g.,software executing on the computer system) analyzes the fields of theform and fills in the form without any user input specifying the answersto the fields. As indicated above, the user may invoke the automaticfilling of the form, but is not involved in the actual filling of theform (e.g., the user is not manually specifying answers to fields butrather they are being automatically completed). The presentspecification provides various examples of operations beingautomatically performed in response to actions the user has taken.

FIGS. 1-3—Communication System

FIGS. 1 and 2 illustrate exemplary (and simplified) wirelesscommunication systems. It is noted that the systems of FIGS. 1 and 2 aremerely examples of certain possible systems, and embodiments may beimplemented in any of various systems, as desired.

The exemplary wireless communication system of FIG. 1 includes a basestation 102A which communicates over a transmission medium with one ormore user equipment (UE) devices 106A, 106B, etc., through 106N. Each ofthe user equipment devices may be referred to herein as a “userequipment” (UE). In the exemplary wireless communication system of FIG.2, in addition to the base station 102A, base station 102B also (e.g.,simultaneously or concurrently) communicates over a transmission mediumwith the UE devices 106A, 106B, etc., through 106N.

The base stations 102A and 102B may be base transceiver stations (BTSs)or cell sites, and may include hardware that enables wirelesscommunication with the user devices 106A through 106N. Each base station102 may also be equipped to communicate with a core network 100 (basestation 102A may be coupled to core network 100A, while base station102B may be coupled to core network 100B), which may be a core networkof a cellular service provider. Each core network 100 may also becoupled to one or more external networks (such as external network 108),which may include the Internet, a Public Switched Telephone Network(PSTN), or any other network. Thus, the base station 102A may facilitatecommunication between the user devices and/or between the user devicesand the network 100A; in the exemplary system of FIG. 2, the basestation 102B may also facilitate communication between the user devicesand/or between the user devices and the network 100B.

The base stations 102A and 102B and the user devices may be configuredto communicate over the transmission medium using any of various radioaccess technologies (RATs), also referred to as wireless communicationtechnologies, or telecommunication standards, such as GSM, UMTS (WCDMA),LTE, LTE-Advanced (LTE-A), 3GPP2 CDMA2000 (e.g., 1×RTT, 1×EV-DO, HRPD,eHRPD), Wi-Fi, WiMAX etc.

For example, base station 102A and core network 100A may operateaccording to a first cellular communication standard (e.g., LTE) whilebase station 102B and core network 100B operate according to a second(e.g., different) cellular communication standard (e.g., GSM, UMTS,and/or one or more CDMA2000 cellular communication standards). The twonetworks may be controlled by the same network operator (e.g., cellularservice provider or “carrier”), or by different network operators. Inaddition, the two networks may be operated independently of one another(e.g., if they operate according to different cellular communicationstandards), or may be operated in a somewhat coupled or tightly coupledmanner.

Note also that while two different networks may be used to support twodifferent cellular communication technologies, such as illustrated inthe exemplary network configuration shown in FIG. 2, other networkconfigurations implementing multiple cellular communication technologiesare also possible. As one example, base stations 102A and 102B mightoperate according to different cellular communication standards butcouple to the same core network. As another example, multi-mode basestations capable of simultaneously supporting different cellularcommunication technologies (e.g., LTE and CDMA 1×RTT, GSM and UMTS, orany other combination of cellular communication technologies) might becoupled to a core network that also supports the different cellularcommunication technologies. Any of various other network deploymentscenarios are also possible.

As a further possibility, it is also possible that base station 102A andbase station 102B may operate according to the same wirelesscommunication technology (or an overlapping set of wirelesscommunication technologies). For example, base station 102A and corenetwork 100A may be operated by one cellular service providerindependently of base station 102B and core network 100B, which may beoperated by a different (e.g., competing) cellular service provider.Thus in this case, despite utilizing similar and possibly compatiblecellular communication technologies, the UE devices 106A-106N mightcommunicate with the base stations 102A-102B independently, possibly byutilizing separate subscriber identities to communicate with differentcarriers' networks.

A UE 106 may be capable of communicating using multiple wirelesscommunication standards. For example, a UE 106 might be configured tocommunicate using either or both of a 3GPP cellular communicationstandard (such as LTE) or a 3GPP2 cellular communication standard (suchas a cellular communication standard in the CDMA2000 family of cellularcommunication standards). As another example, a UE 106 might beconfigured to communicate using different 3GPP cellular communicationstandards (such as two or more of GSM, UMTS, LTE, or LTE-A). Thus, asnoted above, a UE 106 might be configured to communicate with basestation 102A (and/or other base stations) according to a first cellularcommunication standard (e.g., LTE) and might also be configured tocommunicate with base station 102B (and/or other base stations)according to a second cellular communication standard (e.g., one or moreCDMA2000 cellular communication standards, UMTS, GSM, etc.).

Base stations 102A and 102B and other base stations operating accordingto the same or different cellular communication standards may thus beprovided as one or more networks of cells, which may provide continuousor nearly continuous overlapping service to UEs 106A-106N and similardevices over a wide geographic area via one or more cellularcommunication standards.

A UE 106 might also or alternatively be configured to communicate usingWLAN, Bluetooth, one or more global navigational satellite systems(GNSS, e.g., GPS or GLONASS), one and/or more mobile televisionbroadcasting standards (e.g., ATSC-M/H or DVB-H), etc. Othercombinations of wireless communication standards (including more thantwo wireless communication standards) are also possible.

The UE 106 may be a device with wireless network connectivity such as amobile phone, a hand-held device, a computer or a tablet, or virtuallyany type of wireless device.

The UE may include a processor that is configured to execute programinstructions stored in memory. The UE may perform any of the methodembodiments described herein by executing such stored instructions.Alternatively, or in addition, the UE may include a programmablehardware element such as an FPGA (field-programmable gate array) that isconfigured to perform any of the method embodiments described herein, orany portion of any of the method embodiments described herein.

The UE 106 may be configured to communicate using any of multiplewireless communication protocols. For example, the UE 106 may beconfigured to communicate using two or more of GSM, UMTS (W-DCMA,TD-SCDMA, etc.), CDMA2000 (1×RTT, 1×EV-DO, HRPD, eHRPD, etc.), LTE,LTE-A, WLAN, or GNSS. Other combinations of wireless communicationstandards are also possible.

The UE 106 may include one or more antennas for communicating using oneor more wireless communication protocols. The UE 106 may share one ormore parts of a receive and/or transmit chain between multiple wirelesscommunication standards; for example, the UE 106 might be configured tocommunicate using either (or both) of GSM or LTE using a single sharedradio. The shared radio may include a single antenna, or may includemultiple antennas (e.g., for MIMO) for performing wirelesscommunications.

FIG. 3—Example Cellular Network

FIG. 3 illustrates a simplified block diagram of an example cellularnetwork (wireless communication system) that may be particularly usefulfor implementing various of the embodiments described herein. The UE 106may be in communication with a cellular network, where the cellularnetwork may comprise a base station 102 (or eNodeB) and an evolvedpacket core (EPC) 101, as shown. The UE 106 may communicate in awireless manner with the base station 102. In turn, the base station 102may be coupled to a core network, shown in this example embodiment as anevolved packet core (EPC) 101. As shown, the EPC 101 may includemobility management entity (MME) 322, home subscriber server (HSS) 324,and serving gateway (SGW) 326. The EPC 100 may include various otherdevices known to those skilled in the art as well.

Operations described herein as being performed by the cellular network(or NW) may be performed by one or more of the cellular network devicesshown in FIG. 3, such as one or more of base station, 102, MME 322, HSS324, or SGW 326 in EPC 100, among possible others.

FIG. 4—Example Block Diagram of a UE

FIG. 4 illustrates an exemplary block diagram of a UE 106. As shown, theUE 106 may include a system on chip (SOC) 300, which may includeportions for various purposes. For example, as shown, the SOC 300 mayinclude processor(s) 302 which may execute program instructions for theUE 106 and display circuitry 304 which may perform graphics processingand provide display signals to the display 345. The processor(s) 302 mayalso be coupled to memory management unit (MMU) 340, which may beconfigured to receive addresses from the processor(s) 302 and translatethose addresses to locations in memory (e.g., memory 306, read onlymemory (ROM) 350, NAND flash memory 310) and/or to other circuits ordevices, such as the display circuitry 304, radio 330, connector I/F320, and/or display 345. The MMU 340 may be configured to perform memoryprotection and page table translation or set up. In some embodiments,the MMU 340 may be included as a portion of the processor(s) 302.

As shown, the SOC 300 may be coupled to various other circuits of the UE106. For example, the UE 106 may include various types of memory (e.g.,including Flash memory 310), a connector interface 320 (e.g., forcoupling to a computer system, dock, charging station, etc.), thedisplay 345, and wireless communication circuitry 330 (e.g., for GSM,UMTS, LTE, LTE-A, CDMA2000, Bluetooth, Wi-Fi, GPS, etc.).

The UE device 106 may include at least one antenna, and possiblymultiple antennas, for performing wireless communication with basestations and/or other devices. For example, the UE device 106 may useantenna 335 to perform the wireless communication. As noted above, theUE may be configured to communicate wirelessly using multiple wirelesscommunication standards.

The UE 106 may also include one or more user interface elements. Theuser interface elements may include any of various elements, such asdisplay 345 (which may be a touchscreen display), a keyboard (which maybe a discrete keyboard or may be implemented as part of a touchscreendisplay), a mouse, a microphone and/or speakers, one or more cameras,one or more buttons, sliders, and/or dials, and/or any of various otherelements capable of providing information to a user and/orreceiving/interpreting user input.

As shown, the UE 106 may also include two or more subscriber identitymodules (SIMs) 360 and 362. One or both of SIMs 360 and 362 may beimplemented as an embedded SIM (eSIM). In this case, the SIMs 360 and/or362 may be implemented in device hardware and/or software. For example,in some embodiments, the UE 106 may include an embedded UICC (eUICC),e.g., a device which is built into the UE 106 and is not removable. TheeUICC may be programmable, such that one or more eSIMs may beimplemented on the eUICC. In other embodiments, the eSIM may beinstalled in UE 106 software, e.g., as program instructions stored on amemory medium (such as memory 306 or Flash 310) executing on a processor(such as processor 302) in the UE 106. As one example, a SIM 360 may bean application which executes on a Universal Integrated Circuit Card(UICC). Alternatively, or in addition, one or both of SIMs 360 and 362may be implemented as removeable SIM cards.

Each SIM 360 or 362 may include a number of types of information,including personalized information specific to a user and/or device(e.g., personalized information), and information that is not specificto a user and/or device (e.g., common information). The personalizedinformation may include user/unit specific data, for example informationidentifying the user/unit to their carrier's network, personalizedauthorization and/or security information, etc. Some or all of thepersonalized information may be used as a subscriber identity for the UE106, for example in order to identify the UE 106 to a carrier's networkand to obtain cellular service from the carrier.

As one example, the personalized information may include one or moreInternational Mobile Subscriber Identity (IMSI) numbers. An IMSI mayidentify the subscriber to their carrier's network. The IMSI may, forexample, be a number including the subscriber's “home” mobile countrycode (MCC) and mobile network code (MNC), as well as a MobileSubscription Identification Number (MSIN) which is unique to thesubscriber. The personalized information may also or alternativelyinclude a personal identification number (PIN) (e.g., a code which theuser may use to access their SIM), a personal unblocking code and/orpersonal unblocking key (PUC/PUK), and one or more authentication keys(K/Ki). Any of a variety of other personalized information may also oralternatively be used, as desired.

Thus, each SIM 360 and 362 may contain subscriber identity informationthat may be used to identify the UE 106 to its subscriber's carriercellular network. As noted above, the UE 106 may utilize multiplesubscriber identities. For example, a user may consider it desirable toobtain service from multiple carriers for any of a variety of reasons,including differing footprints/service areas of different carriers,different service plans/pricing offered by different carriers, ordifferent technologies used. In some cases it may be desirable toutilize multiple subscriber identities (whether from the same ordifferent carriers) as a means of differentiating types of interactions,such as work-related communications and personal communications.

As a further possibility, a situation might arise in which it might bedesirable to utilize multiple subscriber identities in a single devicefor some carriers which implement LTE networks. In particular, in manycases an LTE (e.g., as a packet-switched communication technology)network may be (at least initially) deployed for data communications(e.g., web browsing, email and other networking applications, etc.),while a (e.g., pre-existing) GSM and/or UMTS (e.g., which may includecircuit-switched communication technologies) network may be utilizedprovided for voice communications.

As further described below, the UE may implement various techniqueswhich enable a particular SIM to perform suspend and resume operationswith the cellular network while reducing disruption due to RRC statemismatch. Accordingly, as described further subsequently herein, the UE106 may include hardware and software components for implementingmethods for improved suspend/resume operations when transitioningbetween use of the different SIMs.

The processor 302 of the UE device 106 may be configured to implementpart or all of the methods described herein, e.g., by executing programinstructions stored on a memory medium (e.g., a non-transitorycomputer-readable memory medium). In other embodiments, processor 302may be configured as a programmable hardware element, such as an FPGA(Field Programmable Gate Array), or as an ASIC (Application SpecificIntegrated Circuit).

FIG. 5—Exemplary Block Diagram of a Base Station

FIG. 5 illustrates an exemplary block diagram of a base station 102. Itis noted that the base station of FIG. 5 is merely one example of apossible base station. As shown, the base station 102 may includeprocessor(s) 404 which may execute program instructions for the basestation 102. The processor(s) 404 may also be coupled to memorymanagement unit (MMU) 440, which may be configured to receive addressesfrom the processor(s) 102 and translate those addresses to locations inmemory (e.g., memory 460 and read only memory (ROM) 450) or to othercircuits or devices.

The base station 102 may include at least one network port 470. Thenetwork port 470 may be configured to couple to a telephone network andprovide a plurality of devices, such as UE devices 106, access to thetelephone network as described above in FIGS. 1 and 2.

The network port 470 (or an additional network port) may also oralternatively be configured to couple to a cellular network, e.g., acore network of a cellular service provider. The core network mayprovide mobility related services and/or other services to a pluralityof devices, such as UE devices 106. In some cases, the network port 470may couple to a telephone network via the core network, and/or the corenetwork may provide a telephone network (e.g., among other UE devicesserviced by the cellular service provider).

The base station 102 may include at least one antenna 434, and possiblymultiple antennas. The at least one antenna 434 may be configured tooperate as a wireless transceiver and may be further configured tocommunicate with UE devices 106 via radio 430. The antenna 434communicates with the radio 430 via communication chain 432.Communication chain 432 may be a receive chain, a transmit chain orboth. The radio 430 may be configured to communicate via variouswireless telecommunication standards, including, but not limited to,LTE, WCDMA, CDMA2000, etc.

The processor 404 of the base station 102 may be configured to implementpart or all of the methods described herein, e.g., by executing programinstructions stored on a memory medium (e.g., a non-transitorycomputer-readable memory medium). Alternatively, the processor 404 maybe configured as a programmable hardware element, such as an FPGA (FieldProgrammable Gate Array), or as an ASIC (Application Specific IntegratedCircuit), or a combination thereof.

The cellular network devices such as shown in FIG. 3 may have a somewhatsimilar architecture as described above, but would typically not includeRF circuitry or an antenna. Thus each of the cellular network devicesshown in FIG. 3 would typically have a processing element and memory forperforming their respective functions.

As used herein, a network or cellular network (e.g., NW1 and/or NW2 asdescribed below) may refer to one or more physical entities containedwithin a network infrastructure to perform the described methods. Forexample, a gNB (or eNB) such as that illustrated in FIG. 5 may directlyreceive indications and messaging from the UE and may relay thesemessages from the UE to an access and mobility management function (AMF)or a mobile management entity (MME) on the Core Network side. The MME(or AMF) may inform the gNB (or eNB) to retain the RRC context of the UE(i.e. a Connected state and/or an established EPS bearer/PDU sessionalong with the QoS details), the MME (or AMF) may start the timer, andif the timer expires before the suspended SIM resumes, the MME (or AMF)may inform the serving gateway (S-GW) or the user plane function (UPF)to release the bearers/PDN contexts for UE as well as inform the eNB (orgNB) to release the UE context (i.e. to forget the C-RNTI and the restof the state information of the UE and consider the UE to be IDLE). Ifthe timer is running and the eNB (or gNB) gets an RRC resume requestfrom the UE, then the eNB (or gNB) may confirm that the C-RNTI existsand that the UE context may be recovered and may forward the Resumerequest to the MME (or AMF), which may inform the S-GW (or UPF) tomodify the radio bearer (e.g., if they had earlier told the S-GW or UPFto freeze their context), stop the timer, and/or continue as if the UEwas connected. Said another way, the combination of eNB-MME-SGW for LTEor gNB-AMF-UPF for 5G NR may be understood as being interconnectedlyinvolved in performing the embodiments described herein.

RRC State Mismatch Avoidance—Problem Statement

As described above, some UE devices may be capable of containingmultiple subscriber identity modules, or SIMs. In some cases, these SIMsmay be Universal SIMs, or USIMs.

Some UE devices with multiple SIMs, i.e., dual-SIM and multi-SIMdevices, including multi-USIM (or MUSIM) devices, may have a singularreceiver (RX) architecture. In other words, some multi-SIM UEs may eachhave only one receiver system for conducting cellular communications fortheir multiple SIMs. Thus in this instance the multiple SIMs on the UEshare the single receiver system (or single radio). For these multi-SIMUEs, it may become necessary for the UE to suspend activity on one SIMwhile undertaking another higher-priority activity on another SIM.

For example, the UE 106 may be a dual-SIM device, i.e., may contain twoSIMs, and may have a single receiver system for the two SIMs. The firstSIM may be configured with a preference for data transfer, and thesecond SIM may be configured with a preference for non-datacommunications, e.g., for circuit-switched (CS) communications, orcellular voice calls.

In a common scenario, the first SIM, i.e., the data SIM, may be engagedin data communications and may be operating in a Connected mode with thenetwork, e.g., via a first radio resource control (RRC) connection. Forexample, the UE may be actively performing data transfer using the firstSIM via the first RRC connection, e.g., for one or more applications onthe UE, such as an Internet browsing application and/or one or morebackground applications. In this scenario, the second SIM, i.e. thenon-data SIM instance, may be operating in Idle mode.

The UE may then receive a page or user input indicating ahigher-priority communication to be conducted via the second SIM. Forexample, the UE may receive a mobile terminated (MT) voice call from thenetwork, a user of the UE may initiate a mobile originated (MO) voicecall, or the UE may receive or send an SMS (Short Message Service)message or other circuit-switched (CS) communication.

In response to the indication for higher-priority communication on thesecond SIM, the UE may perform a local suspension of the first RRCconnection of the first SIM, i.e., may suspend data communications onthe first SIM, in order to make the UE's receiver available to conductthe higher-priority communication on the second SIM.

When the higher-priority communication on the second SIM is completed(e.g., in the case of a voice call, because the user terminated thecall), the second SIM may return to Idle mode. The UE may then operateto resume the previously suspended first RRC connection using the firstSIM.

Problems may arise at this point if the network is no longersynchronized with the UE regarding the state of the first RRCconnection.

The resumption of the suspended first RRC connection may be performedaccording to a resumption sequence, e.g. via an RRC ConnectionReestablishment request. In some cases, this resumption sequence may notbe in synchronization with the network, which may have developed anincompatible perception of the first RRC connection after the first RRCconnection was suspended. This lack of synchronization may impact thethroughput performance on the first SIM, and may lead to missed pagingmessages during resumption and re-establishment procedures.

In some cases, the network may not have received an appropriateindication that the first SIM had transitioned into Idle mode (when theUE earlier suspended communication on the first SIM), and hence may beunprepared for the resumption sequence.

In one set of undesirable scenarios, the network may contain obsoleteinformation indicating that the first SIM is still in its originalConnected mode, even after the first SIM has transitioned into Idlemode. Hence, the network may attempt to page the UE on the first SIM,e.g., for an MT voice call, even though the UE is in Idle mode. This canresult in missed pages and/or dropped or failed calls. The network mayalso be wasting network resources such as uplink and downlink resourcesby allocating them to the first RRC connection (i.e., the first SIM onthe UE), even though the first RRC connection is inactive and henceunable or unprepared to receive these communications.

In a second set of undesirable scenarios, the network may have droppedthe first RRC connection with the first SIM at some point after thefirst SIM (i.e., the first RRC connection) transitioned to Idle mode. Ifthe first SIM attempts to re-establish the first RRC connection in orderto perform or resume certain data communications, the network may thenbe unable to receive its communications. The UE may then need to performprocedures to establish a new connection with the network in order toperform these communications. Thus, the first SIM may be unable topromptly resume data communications via the first RRC connection. Thismay lead to data transfer failures and long delays (increased latency)for the user of the UE.

Producers and vendors of multi-SIM and MUSIM devices have implementedvarious proprietary solutions to handle some of these above-mentionedscenarios and associated problems. However, these solutions must bevalidated across and adjusted for many different deployments around theworld in order to ensure adequate performance, which may demand aconsiderable amount of effort and resources. Therefore, improvements inthe field are desired. In particular, a 3GPP-defined solution would bedesirable to address these and other problems.

UE Indicates Suspend/Renewal Operations to the Network for RRC StateSynchronization

In some embodiments, in a scenario such as that described above where afirst SIM is suspended so that a second SIM can perform a higherpriority task, the first SIM which is being suspended (or the softwarestack executing and using the first SIM) can gracefully indicate to theNW using a “lightweight” mechanism (a relatively minor amount ofsignaling”, that it being suspended for another high priority activityon the other SIM instance

Alternatively, during resumption when the second SIM has completed thehigher priority task and relinquished use of the radio, and the firstSIM is resuming a Connected state to resume its data transfers, thefirst SIM that is requesting resumption could inform the cellularnetwork at that time that this resumption is after a local suspensiondue to a high priority activity on the other SIM instance.

One motivation or goal in performing the above method is to avoid RRCstate mismatch between the UE and the network, and more particularly,between both the first and second SIMs and their respective cellularnetworks.

In one embodiment, the first SIM which is about to be suspended canrequest for a temporary transition to the RRC Inactive state, and theconnection state or context of the SIM is stored and maintained at thenetwork side while the other high priority activity is completed on thefirst SIM. The connection state or context of the first SIM is storedand maintained at the network side so that the network can quicklyrestore the connection state of the first SIM when the second SIMcompletes its higher priority task.

For example, in storing the UE context, we may refer to herein that theNW may store one or more of a UE identifier such as the UE ID (i.e.C-RNTI); a state the UE was in (e.g., Connected); a time when the SIM1was suspended; and/or packet data networks (PDNs), evolved packet system(EPS) bearers, and/or packet data unit (PDU) sessions that wereestablished when the UE was in Connected mode and their quality ofservice (QoS) and/or QoS Flow Identifier (QFI) thereof. Using thisstored information, when the SIM1 connection is resumed, the NW mayallocate the physical and transport channel resources to the UE for thePDN/EPS bearer/PDU sessions and for the QoS/QFI configured earlier andmay resume the data transfer.

The conveyance or communication of information regarding SIMsuspension/resumption between the UE and the cellular network may resultin less paging failures on the suspended SIM, since the network is nowaware of the suspension status of the SIM. Further, these methodsprovide for a faster and more efficient resumption of the suspended SIMwith a reduced chance of the network rejecting the resumption due to apotential RRC state mismatch,

These methods are described in greater detail below.

FIG. 6—UE Provides Indications to the Network for RRC StateSynchronization (Resume without Timeout)

FIG. 6 is a message sequence chart illustrating a method for UE with twoSIMs to coordinate with the network (or provide indications to thenetwork) regarding its SIM suspend/resume operations for improved RRCstate synchronization.

The message sequence chart of FIG. 6 illustrates the various messagingbetween a first communication software stack (UE Stack 1, 602) operatingwith a first SIM, a second communication software stack (UE Stack 2,604) operating with a second SIM, a first cellular network (NW 1, 606)and a second cellular network (NW 2, 608). The first communicationsoftware stack (UE Stack 1) operating with the first SIM may communicatewith NW 1, and the second communication software stack (UE Stack 2)operating with the second SIM may communicate with NW 2. The term“communication software stack” refers to software executing on the UEwhich enables the UE to communicate with a network. In some embodiments,the UE maintains a communication software stack for each of the twoSIMs, i.e., the UE maintains a first communication software stack thatexecutes in conjunction with the first SIM (SIM 1) to perform cellularcommunication using the first SIM, and UE maintains a secondcommunication software stack that executes in conjunction with thesecond SIM (SIM 1) to perform cellular communication using the secondSIM.

As shown, at 610 UE Stack 1 may be in RRC Connected mode performing datatransfers with NW 1 using the radio (RF) of the UE 106. NW 1 may also bein Connected mode since it is communicating with UE Stack 1. Since theUE contains only a single radio, when the radio is being used by UEStack 1, then UE Stack 2 is in RRC Idle mode at 612.

At 614, a high priority activity is triggered on UE Stack 2, whereinthis high priority activity triggered on UE Stack 2 requires suspensionof current activity on UE Stack 1. For example, UE Stack 1 may beengaged in RRC Connected mode performing data transfers with NW 1, and avoice call may be activated on UE Stack 2. In other words, a voice callmay be initiated (or received) by the UE, wherein the voice call ishandled by UE Stack 2. For example, a mobile originating (MO) call maybe made or placed by the user of the UE, where the MO call is handledusing UE Stack 2. Alternatively, a mobile terminating (MT) call may bereceived by the UE, where the MT call is handled using UE Stack 2.

In response to this higher priority activity being initiated on UE Stack2, at 616 UE Stack 2 may send a suspend request to UE Stack 1 to notifyUE Stack 1 that it needs to suspend operations.

In response to the notification from UE Stack 2, at 618 UE Stack 1 maythen transmit an RRC Connection Suspend Request to the cellular networkto which UE Stack 1 is connected, (NW 1). The RRC Connection SuspendRequest may comprise information that specifies the cause of the suspendrequest. More specifically, the RRC Connection Suspend Request maycomprise information that specifies that the suspend request is due to ahigher priority activity being initiated on another SIM of the UE. Thecause information may take the form of a code, such as “MUSIM HighPriority” or something similar.

As shown, receipt of the RRC Connection Suspend Request from UE Stack 1may cause the NW 1 to transmit an RRC Connection Suspend message at 620back to UE Stack 1. The RRC Connection Suspend message may include acode or instruction that specifies that UE Stack 1 should transitionfrom Connected mode to Inactive mode. This code or instruction may takethe form of “suspend state=RRC_INACTIVE” or something similar. Thepresence of this code in the RRC Connection Suspend message instructs UEStack 1 to enter the Inactive state. In other words, the “suspend state”code is used to indicate the new RRC state for UE Stack 1.

The RRC Connection Suspend message may also include a code orinstruction that specifies a timer duration for a suspend timeroperating on the UE. This code or instruction may take the form of“suspend_timer_duration=X”. As discussed further below, the suspendtimer duration may specify an amount of time during which the UE Stack 1will remain in RRC Inactive mode before transitioning to RRC Idle mode.Typical values for the suspend timer duration may range from severalminutes or seconds to several hours.

In response to UE Stack 1 receiving the RRC Connection Suspend messagefrom NW 1, UE Stack 1 is suspended at 622 and thus UE Stack 1 may enterRRC Inactive mode at 624 to facilitate or enable the higher priorityactivity on UE Stack 2. Receipt of the RRC Connection Suspend messagemay also trigger the start of the suspend timer on the UE.

In some embodiments, NW 1 may also include a similar suspend timer, andtransmission of the RRC Connection Suspend message may cause NW 1 tostart its own suspend timer. Thus both UE Stack 1 (the UE) and NW 1 maystart its own respective suspend timer to determine how long the RRCconnection between UE Stack 1 and NW 1 remains in Inactive mode beforetiming out and transitioning to RRC Idle mode.

As shown, triggering of the high priority activity on UE Stack 2 causesUE Stack 2 to enter RRC Connected mode at 626. UE Stack 2 may thenperform the higher priority activity at 628, e.g., a voice call.

In the exemplary embodiment of FIG. 6, the high priority activity on UEStack 2 (the voice call) is completed at 628 before the suspend timerexpires. Upon completion of the high priority activity on UE Stack 2, UEStack 2 enters RRC Idle mode at 630. UE Stack 2 may then notify UE Stack1 at 632 that the high priority activity on UE Stack 2 has beencompleted and UE Stack 2 is now in Idle mode. In response, UE Stack 1may transmit an RRC Connection Resume Request at 634 to NW 1. NW 1receives the RRC Connection Resume Request and in response transmits anRRC Connection Reconfiguration message at 636 back to UE Stack 1. UEStack 1 receives the RRC Connection Reconfiguration message and inresponse enters RRC Connected mode. UE Stack 1 then transmits an RRCConnection Reconfiguration Complete message at 638 back to NW 1, therebyentering the RRC Connected mode.

FIG. 7—Message Flow Diagram—UE Provides Indications to the Network forRRC State Synchronization (Resume with Timeout)

FIG. 7 is a message sequence chart illustrating a method for UE with twoSIMs to coordinate with the network (or provide indications to thenetwork) regarding its SIM suspend/resume operations for improved RRCstate synchronization. Like FIG. 6, FIG. 7 describes communicationbetween a UE Stack 1 702 and NW1 706, as well as communication betweenUE Stack 2 704 and NW2 708. FIG. 7 is similar to FIG. 6, except thatFIG. 7 illustrates the case where the suspend timer expires prior tocompletion of the high priority activity over UE Stack 2. For example,each of steps 710-726 may proceed similarly to steps 610-626 of FIG. 6.

However, the procedure outlined in FIG. 7 differs from FIG. 6 beginningat step 728. Specifically, at 728, the suspension timer expires and UEStack 1 enters an RRC Idle state at 730 prior to completion of the highpriority activity over UE Stack 2 at 732.

Accordingly, at 734, UE Stack 1 may resume its connection with NW 1 at734 by setting up a new RRC Connection. At 738, UE Stack 1 transmits anRRC Connection Resume Request to NW 1. At 740, NW 1 responds to UE Stack1 with an RRC Connection Setup message, and UE Stack 1 subsequentlyresponds to NW 1 at 742 with an RRC Connection Setup Complete message toenter the RRC Connected state with NW 1 at 744.

FIG. 8—Network Stores Connected State Context to Maintain SynchronousRRC States

FIG. 8 is a message sequence chart which illustrates an alternativeembodiment. Similar to FIGS. 6 and 7, the message sequence chart of FIG.8 illustrates the various messaging between a first communicationsoftware stack operating with a first SIM (SIM1), 802, a secondcommunication software stack operating with a second SIM (SIM2), 804,and the cellular network (NW(SIM1)) 806 communicating with the firstSIM. The first communication software stack operating with SIM1 may bein Connected mode 808, 812, performing data transfers with NW(SIM1)using the radio (RF) of the UE 106. As shown, the Network NW(SIM1) isalso in Connected mode since it is communicating with the firstcommunication software stack. Since the UE contains only a single radio,when the radio is being used by SIM1 (used by the first communicationsoftware stack operating with SIM1), then SIM2 (the second communicationsoftware stack operating with SIM2) is in Idle mode 810. In thefollowing discussion, the term “SIM1” is used to refer to the firstcommunication software stack operating in conjunction with SIM1, andsimilarly “SIM2” is used to refer to the second communication softwarestack operating in conjunction with SIM2.

At 814, a voice call is initiated (or received) by SIM2. As shown inthis example, a mobile originating (MO) call is made or placed by theuser of the UE, where the MO call is performed using SIM2. In responseto the MO call being initiated, SIM2 transmits a Suspend Request at 816to SIM1. In response to the Suspend Request, SIM1 transmits an RRCSuspend Request at 818 to the cellular network to which SIM1 isconnected, NW(SIM1). In the embodiments of FIGS. 6 and 7, receipt of aSuspend Request from SIM1 would cause the NW(SIM1) to transmit a suspendmessage back to SIM1, including a prescription for SIM1 to go to aninactive state and a timer duration value as described above. However,in the embodiment of FIG. 8, rather than transmitting such a suspendmessage back to the UE (SIM1), instead the network “freezes” the context(or connection state) of the current Connected mode of SIM1 at 822. Inother words, the network NW(SIM1) stores the current Connected modeparameters/data relating to the context or connection state of SIM1 inmemory and preserves this stored context for later use (in restoringConnected mode). In addition, in response to receipt of the SuspendRequest from SIM1, the network also suspends or prevents mobileterminating (MT) calls and downlink data from being transferred to SIM1at 826. In other words, since NW(SIM1) knows that SIM1 will not bereachable for a period of time, i.e., that SIM1 will not be able toreceive communications for a period of time (because it is requesting tobe suspended), NW(SIM1) configures itself such that it will not send anydownlink notifications of paging to SIM1 for a period of time, andfurther that NW(SIM1) will not schedule any new data for SIM1. As analternative to the above, e.g., if the network does not support thisfeature, the NW(SIM1) can send an RRC Connection Release message to SIM1to place SIM1 in either the Inactive or Idle state, and suspend pagingto SIM1, and the NW(SIM1) can also enter to a similar Inactive or Idlestate.

In response to the MO call being made using SIM2, SIM2 enters aConnected state at 820, and a voice call is performed, which may involvea second different cellular network. At 824, the voice call being madeusing SIM2 ends, and SIM2 returns to an Idle state at 828. After theSIM2 goes back to an Idle state, SIM2 sends a Resume Request message toSIM1 at 830. In response to receiving the Resume Request from SIM1, SIM2then sends an RRC Resume Request to NW(SIM1) at 832. The RRC ResumeRequest sent by SIM1 may contain information indicating that this is aresumption from a situation involving a higher priority connection thatnecessitated another SIM on the UE to assume control of the radio. Whenthe network NW(SIM1) receives the RRC Resume Request from SIM1, thenetwork may respond in one of a plurality of different manners.

In one embodiment, the NW(SIM1) may restored the connection state orcontext of the previous Connected mode connection at 834, i.e., theconnection state that was previously “frozen” at step 822. This enablesthe previous Connected mode to “resume” from where it left off. TheNW(SIM1) may also resume (or discontinue the suspension of) mobileterminating calls and downlink data transfers to SIM1. NW(SIM1) may alsosend an RRC Resume message to SIM1 at 838 to notify SIM1 that the priorConnected mode has been resumed. Thus in this embodiment, the NW(SIM1)and SIM1 may both return to Connected mode (Connected state) at 840 and842, and data transfer, MT calls, and paging are now operational as theynormally would be in Connected mode.

In another embodiment, it may be the case that a significant period oftime may have elapsed during which the connection to SIM1 has beensuspended. For example, the MO voice call performed by SIM2 may havelasted longer than a specified period of time (e.g., as determined by atimer used for this purpose). In this case, the NW(SIM1) may havediscarded the stored Connected mode context upon the expiration of atimer (and then of course the network would no longer have storedConnected mode parameters to restore). In this instance, when thiscertain period of time has elapsed, the NW(SIM1) may transition toeither Idle or Inactive mode at 844, 846, and discard (no longer store)the previously stored Connected mode context. The NW(SIM1) may alsotransmit an RRC Connection Release message to SIM1 at 848. This messagemay also indicate to SIM1 that it should transition to Idle mode aswell, which it may perform at 850. In this case, a new connection mayneed to be reestablished between SIM1 and NW(SIM1) in order to enabledata communication between them.

An important benefit to the above method is that this ensures that thereis no discrepancy in the RRC states between the network and the UE. Inaddition, the network suspends paging and downlink data to the suspendedSIM, thus preventing any problems associated with attempting tocommunicate with a suspended device. Further, the network maintains fullcontrol over the UE's RRC state, and thus the network ensures that bothSIMS of the UE remain in synch with the RRC state of the network, i.e.,that the RRC state of the SIMS matches that of the network at all times.

RRC State Mismatch in 5G NR

FIG. 9 is a message sequence chart which illustrates issues that mayarise in some existing implementations of a DSDS device. Similar toFIGS. 6-8, the message sequence chart of FIG. 9 illustrates the variousmessaging between a first communication software stack operating with afirst SIM (SIM1 902), a second communication software stack operatingwith a second SIM (SIM2 904), and the cellular network (NW(SIM1) 906)communicating with the first SIM. However, FIG. 9 may be moreparticularly applicable to 5G NR implementations which utilize an RRCInactive state. The first communication software stack operating withSIM1 may be in Connected mode 908 performing data transfers withNW(SIM1) using the radio (RF) of the UE 106. As shown, the NetworkNW(SIM1) is also in Connected mode 912 since it is communicating withthe first communication software stack. Since the UE contains only asingle radio, when the radio is being used by SIM1 (used by the firstcommunication software stack operating with SIM1), then SIM2 (the secondcommunication software stack operating with SIM2) is in Idle mode 910.In the following discussion, the term “SIM1” is used to refer to thefirst communication software stack operating in conjunction with SIM1,and similarly “SIM2” is used to refer to the second communicationsoftware stack operating in conjunction with SIM2.

At 914, the NW(SIM1) may transmit an RRC connection release message toSIM1, to transition the connection between SIM1 and NW(SIM1) fromConnected mode to Inactive mode. SIM1 and NW(SIM1) may then bothtransition their mutual connection to the Inactive mode.

At 918, a voice call is initiated (or received) by SIM2. As shown inthis example, a mobile originating (MO) call is made or placed by theuser of the UE, where the MO call is performed using SIM2, which may bea high priority call. In response to the MO call being initiated, SIM2transmits a Suspend Request 922 to SIM1 to indicate that SIM2 would liketo take over the RF chain of the UE to implement the MO call.

At 924, SIM2 may enter an RRC Connected state with its cellular network(e.g., NW(SIM2), not shown in FIG. 9), and may conduct the MO call witha remote entity over NW(SIM2). The MO call may be conducted for a longperiod of time (e.g., several hours or another long period of time)before the call is ended at 926 and the connection between SIM2 andNW(SIM2) transitions to the Idle state at 928.

After SIM1 receives the resume request from SIM2 at 930, one of twoalternative procedures may occur which are illustrated in the two largeboxes corresponding to steps 932-942 and steps 944-952, respectively. Inthe first alternative, when SIM1 receives the resume request from SIM2at 930, the UE may assume that it is in an Inactive state 934 withNW(SIM1), while NW(SIM1) assumes that the UE is in an Idle state 936. Inother words, there may be a mismatch between the UEs and NW(SIM1)'sunderstanding of the state of the connection between SIM1 and NW(SIM1).As one example, the MO call over SIM2 may have lasted long enough suchthat NW(SIM1) has abandoned the context associated with its connectionwith SIM1 and transitioned the connection to Idle state, while the UEthinks that the connection is in the Inactive state. For example, theNW(SIM1) may have attempted to page SIM1 during the SIM2 call, and mayhave timed out the connection with SIM1 because it did not receive atimely response from SIM1. In these embodiments, SIM1 may have UL datato transmit at 938 and may transmit an RRC resume request with aninactive radio network temporary identifier (I-RNTI) indicator toNW(SIM1) at 940 to resume transmission of the UL data. However, becauseNW(SIM1) no longer holds the context of the connection, NW(SIM1) mayrespond with an RRC release message at 942 to release the RRCconnection, increasing latency of the UL transmission.

In the second alternative illustrated in reference to steps 944-952, analternative mismatch may exist between the assumptions of the connectionstatus by SIM1 and NW(SIM1). For example, the UE may assume theconnection between SIM1 and NW(SIM1) has been terminated and is in anIdle state at 946, while NW(SIM1) may maintain the connection context inan Inactive mode at 948. In these embodiments, if SIM1 has UL data totransmit to NW(SIM1) at 950, it may transmit an RRC Connection Requestto NW(SIM1) at 952 to establish a new connection, thus causing highlatency during the setup of a new RRC connection. Embodiments describedbelow present methods and devices to reduce the latency and batterydrain introduced in both of these alternatives.

Utilization of Suspension Timer to Avoid RRC State Mismatch

FIG. 10 is a message sequence chart which illustrates methods anddevices that utilize a suspension timer to enhance operation of a DSDSdevice, according to some embodiments. More specifically, FIG. 10 is amessage sequence chart that address some of the limitations andlatencies introduced in the message sequence chart illustrated in FIG.9. Similar to FIGS. 6-9, the message sequence chart of FIG. 10illustrates the various messaging between a first communication softwarestack operating with a first SIM (SIM1 1002), a second communicationsoftware stack operating with a second SIM (SIM2 1004), and the cellularnetwork (NW(SIM1) 1006) communicating with the first SIM. However, FIG.10 may be more particularly applicable to 5G NR implementations whichutilize an RRC Inactive state. The first communication software stackoperating with SIM1 may be in Connected mode 1008 performing datatransfers with NW(SIM1) using the radio (RF) of the UE 106. As shown,the Network NW(SIM1) is also in Connected mode 1012 since it iscommunicating with the first communication software stack. Since the UEcontains only a single radio, when the radio is being used by SIM1 (usedby the first communication software stack operating with SIM1), thenSIM2 (the second communication software stack operating with SIM2) is inIdle mode 1010. In the following discussion, the term “SIM1” is used torefer to the first communication software stack operating in conjunctionwith SIM1, and similarly “SIM2” is used to refer to the secondcommunication software stack operating in conjunction with SIM2.

Steps 1008-1022 of FIG. 10 may operate similarly to steps 908-922 ofFIG. 9, whereby a connection between SIM1 and NW(SIM1) transitions froma Connected state to an Inactive state. Alternatively, in someembodiments, the network may not support the Inactive state and maytransition the connection SIM1 and NW(SIM1) to an Idle state (not shownin FIG. 10). Subsequently, SIM2 transitions its connection with NW(SIM2)away from an Idle state to initiate a MO call, and SIM2 transmits asuspend request to SIM1 to obtain access to the shared RF chain of theUE. However, subsequent steps of FIG. 10 diverge from that illustratedin FIG. 9.

In particular, at 1024, SIM1 may transmit an RRC suspend request toNW(SIM1) with a MUSIM_suspended cause indication, to indicate toNW(SIM1) that SIM1 is entering a suspended Inactive state. At 1026,NW(SIM1) may respond by transmitting an RRC connection release messageto SIM1 with an RRC_Inactive indication, an I-RNTI, and/or an indicationof a suspension timer duration. The UE and NW(SIM1) may both initiate asuspension timer responsive to the transmission of the RRC connectionrelease at step 1026, and SIM2 may establish a Connected state withNW(SIM2) at 1028 to conduct the MO call.

Subsequently, one of two alternative procedures may be implemented,depending on whether the MO call over SIM2 has ended by the time thesuspend timer has expired, as described in the two large boxes of FIG.10 related to steps 1030-1036 and 1038-1056, respectively.

In the first alternative, the suspend timer may expire and the SIM2 callmay end subsequent to expiry of the suspend timer at 1030. AT 1032, SIM2may transmit a resume request to SIM1. However, because the suspendtimer has expired, the UE may realize that the connection between SIM1and NW(SIM1) has been terminated, and both the UE and NW(SIM1) mayconsider their connection to be in an Idle state. Accordingly, to resumecommunication over SIM1 with NW(SIM1), SIM1 may initiate a new RRCconnection with NW(SIM1) without a mismatch in connection status betweenthe UE and NW(SIM1).

In the second alternative, the SIM2 call may end at 1038 and theconnection between SIM2 and NW(SIM2) may enter an idle state at 1040prior to expiration of the suspend timer. In these embodiments, SIM2 maytransmit a resume request to SIM1 at 1044, and SIM1 may assume that theconnection between SIM1 and NW(SIM1) remains in the Inactive state at1046. Accordingly, at 1050, SIM1 may transmit an RRC resume request toNW(SIM1), including an I-RNTI and a nextStatePreference indicator. ThenextStatePreference indicator may indicate a preferred state of the UEfor the connection between SIM1 and NW(SIM1). For example, if the UE hasremaining UL data that it would like to transmit over SIM1, it mayrequest to transition the SIM1/NW(SIM1) connection to a Connected stateto transmit the UL data. Alternatively, if the UE has no further data totransmit over SIM1, the nextStatePreference indicator may indicate apreference for either an Inactive or an Idle state, according to variousembodiments. Because NW(SIM1) also maintains the suspend timer, itmaintains the connection context with SIM1 in an Inactive state when itreceives the RRC resume request from SIM1. Accordingly, NW(SIM1) mayrespond to SIM1 with either an RRC Resume or an RRC ConnectionReleasemessage, depending on the nextStatePreference indicator and/ornetwork-side considerations. At 1054 and 1056, SIM1 and NW(SIM1) mayproceed to operate according to the next state (e.g., either Connectedmode, Inactive mode, or Idle mode).

Network Coordination to Avoid RRC State Mismatch

FIG. 11 is a message sequence chart which illustrates methods anddevices that utilize network-side coordination to enhance operation of aDSDS device, according to some embodiments. More specifically, FIG. 11is a message sequence chart that utilizes network-side coordination toimprove RRC connection state matching between a network and a UE for aDSDS device. Similar to FIGS. 6-10, the message sequence chart of FIG.11 illustrates the various messaging between a first communicationsoftware stack operating with a first SIM (SIM1 1102), a secondcommunication software stack operating with a second SIM (SIM2 1104), afirst cellular network (NW(SIM1) 1106) communicating with the first SIM,and a second cellular network (NW(SIM2) 1108) communicating with thesecond SIM. FIG. 11 may be more particularly applicable to 5G NRimplementations which utilize an RRC Inactive state. The firstcommunication software stack operating with SIM1 may be in Connectedmode 1110 performing data transfers with NW(SIM1) using the radio (RF)of the UE 106. As shown, the Network NW(SIM1) is also in Connected mode1114 since it is communicating with the first communication softwarestack. Since the UE contains only a single radio, when the radio isbeing used by SIM1 (used by the first communication software stackoperating with SIM1), then SIM2 (the second communication software stackoperating with SIM2) is in Idle mode 1112, and NW(SIM2) may likewise bein Idle mode 1116 in regard to its connection with SIM2. In thefollowing discussion, the term “SIM1” is used to refer to the firstcommunication software stack operating in conjunction with SIM1, andsimilarly “SIM2” is used to refer to the second communication softwarestack operating in conjunction with SIM2.

Steps 1110-1126 of FIG. 11 may operate similarly to steps 908-922 ofFIG. 9 and steps 1008-1022 of FIG. 10, whereby a connection between SIM1and NW(SIM1) transitions from a Connected state to an Inactive state.Alternatively, in some embodiments, the network may not support theInactive state and may transition the connection between SIM1 andNW(SIM1) to an Idle state (not shown in FIG. 11). Subsequently, SIM2transitions its connection with NW(SIM2) away from an Idle state toinitiate a MO call, and SIM2 transmits a suspend request to SIM1 toobtain access to the shared RF chain of the UE. However, subsequentsteps of FIG. 11 diverge from that illustrated in FIGS. 9 and 10.

In particular, at 1128, SIM2 may initiate an RRC ConnectionEstablishment procedure with NW(SIM2) and enter an RRC Connected stateat 1130. At 1132, NW(SIM2) may notify NW(SIM1) that the Inactive modeconnection between SIM1 and NW(SIM1) should enter a suspended Inactivestate. In response, at 1134, NW(SIM1) may freeze its Inactive modeconnection with SIM1 and initiate a guard timer.

Subsequently, one of two alternative procedures may be implemented,depending on whether the MO call over SIM2 has ended by the time theguard timer has expired, as described in the two large boxes of FIG. 11related to steps 1136-1152 and 1154-1166, respectively.

In the first alternative, the SIM2 call may end at 1138 and 1140, priorto expiration of the suspend timer. At 1142, NW(SIM2) may send a Resumeindication to NW(SIM1), indicating that NW(SIM1) may resume itsconnection with SIM1. In response, at 1144 NW(SIM1) may transmit an SIM1state indicator to NW(SIM2) indicating a preferred RRC state with whichto resume its connection for SIM1. For example, in FIG. 11 the SIM1state indicator indicates a preference for the RRC Inactive state, butNW(SIM1) may also indicate a preference for an RRC Connected state or anRRC Idle state, as desired.

At 1146, NW(SIM2) may transmit an RRC Connection Release message to SIM2to release the connection between NW(SIM2) and SIM2 so that SIM2 mayenter Idle mode. Importantly, NW(SIM2) may include the SIM1 preferredstate indicator in the RRC Connection Release message, thereby informingSIM2 of the preferred RRC state for the connection between SIM1 andNW(SIM1). Advantageously, this may preserve state coordination betweenSIM1 and NW(SIM1) without expending additional radio resources bysending coordination messages between SIM1 and NW(SIM1).

At 1148, SIM2 may send a resume request to SIM1 indicating that SIM2 isrelinquishing access to the RF chain of the UE to SIM1, and may includethe SIM1 preferred state indicator in the resume request (e.g., SIM2indicates to SIM1 that NW(SIM1) would like to resume its connection withSIM1 in the Inactive mode in FIG. 11, although the SIM1 preferred stateindicator may also indicate a preference for either the Connected modeor the Idle mode, as desired). Finally, at 1150 and 1152, both SIM1 andNW(SIM1) may resume their connection without a suspension according tothe preferred state indicator. Accordingly, to communication over SIM1with NW(SIM1) may be resumed without a mismatch in connection statusbetween the UE and NW(SIM1).

In the second alternative described in reference to steps 1154-1166, theguard timer may first expire and the SIM2 call may end at 1156subsequent to expiry of the suspend timer. At 1158, NW(SIM1) maytransition its connection with SIM1 from the Inactive state to the Idlestate responsive to expiry of the guard timer. At 1160, subsequent tothe call between SIM2 and NW(SIM2) ending at 1156, NW(SIM2) may send aSIM1 Resume indicator to NW(SIM1), indicating that NW(SIM2) has endedits MO call with SIM2 such that NW(SIM1) may resume its connection withSIM1. However, since NW(SIM1) has already entered the Idle mode withrespect to its connection with SIM1 and no longer holds the context forthe connection, NW(SIM1) responds to NW(SIM2) with a preferred SIM1state indicator indicating a preference for the RRC Idle state. Similarto step 1146 described above, at 1164 NW(SIM) send an RRC ConnectionRelease message to SIM2 including the SIM1 preferred state indicatorindicating a preference for SIM1 to enter the Idle state. Finally, at1142 SIM2 may send a resume request to SIM1 indicating that SIM2 isrelinquishing access to the RF chain of the UE to SIM1, and furtherincluding the SIM1 preferred state indicator for the Idle state,whereupon SIM1 enters the Idle state at 1166. Accordingly, SIM1 andNW(SIM1) will both have transitioned to the Idle state, thus avoiding astate mismatch regarding their connection without explicitly sendingcoordination messages between SIM1 and NW(SIM1).

FIG. 12—UE Informing Network of Connection Release

FIG. 12 is a message sequence chart which illustrates an alternativeembodiment. Similar to FIGS. 6-11, the message sequence chart of FIG. 12illustrates the various messaging between a first communication softwarestack operating with a first SIM (SIM1), 1202, a second communicationsoftware stack operating with a second SIM (SIM2), 1204, the cellularnetwork (NW(SIM1)) 1206 communicating with the first SIM, and thecellular network (NW(SIM2)) 1208 communicating with the second SIM. Thefirst communication software stack operating with SIM1 may be inConnected mode 1210, 1214, performing ongoing data transfers 1216 withNW(SIM1) using the radio (RF) of the UE 106, while SIM2 is in an Idlestate with regard to its connection with NW(SIM2). As shown, the NetworkNW(SIM1) is also in Connected mode since it is communicating with thefirst communication software stack of SIM1. Since the UE contains only asingle radio, when the radio is being used by SIM1 (used by the firstcommunication software stack operating with SIM1), then SIM2 (the secondcommunication software stack operating with SIM2) is in Idle mode 1210.In the following discussion, the term “SIM1” is used to refer to thefirst communication software stack operating in conjunction with SIM1,and similarly “SIM2” is used to refer to the second communicationsoftware stack operating in conjunction with SIM2.

In some embodiments, when a non-data-preferred SIM (e.g., SIM1) ends avoice call, it will relinquish the RF chain of the UE to thedata-preferred SIM (e.g., SIM2) so that SIM2 may continue a datatransfer procedure that was suspended due to the SIM1 voice call. Inthis case, there may be an RRC state mismatch between SIM1 and NW(SIM1)since the UE may typically perform only a local release of the RRCConnection on SIM1 and may cause a mismatch with NW(SIM1). Subsequently,if a MO user triggers back to back voice calls on SIM1, the 2nd call maybe missed due to the RRC state mismatch. To address these and otherconcerns, FIG. 12 presents a method for the UE to inform the NW of aconnection release to avoid a potential RRC state mismatch.

While the data transfer 1216 is ongoing between SIM1 and NW(SIM1), ahigh priority call may be initiated or received by SIM2 at 1218. Inresponse, at 1220, SIM2 may send a suspend request to SIM1 so that SIM2can obtain access to the radio of the UE. SIM2 may then establish aconnection with NW(SIM2) at 1224 and 1226 to conduct the high prioritycall, and SIM1 may enter a suspended state at 1222.

The high priority call may end at 1228, and SIM2 may send a SignalingConnection Release Indication to NW(SIM2) at 1230 to inform the networkthat SIM2 is entering the Idle state at 1232. Correspondingly, inresponse to receiving the Signaling Connection Release Indication fromSIM2, NW(SIM2) may also enter an Idle state with respect to itsconnection SIM2, such that SIM2 and NW(SIM2) are in sync with respect totheir mutual connection state.

At 1236, in response to entering the Idle state, SIM2 may send a ResumeRequest to SIM1 so that SIM1 may resume its connection with NW(SIM1),and SIM1 may attempt to reestablish its RRC Connection with NW(SIM1) at1238.

At this point, one of two alternative embodiments may be implemented,depending on whether the attempt to reestablish a connection betweenSIM1 and NW(SIM1) is successful. If reestablishing the connection issuccessful 1240, the connection may be established at 1242 and 1244, andSIM1 and NW(SIM1) may continue to transfer data in uplink and/ordownlink. alternatively, if the attempt to reestablish the connectionbetween SIM1 and NW(SIM1) is unsuccessful at 1248, both SIM1 andNW(SIM1) may enter the Idle state with regard to their mutualconnection.

At 1254, NW(SIM2) may be notified of an incoming call for SIM2 at 1254,and NW(SIM2) may page SIM2 in Idle mode for the mobile-terminated (MT)call at 1256. Accordingly, SIM2 may establish the MT call at 1258.

The following paragraphs describe additional embodiments of theinvention.

A cellular network device may comprise a processing element; and amemory coupled to the processing element; wherein the cellular networkdevice is configured to: establish a first radio resource control (RRC)connection with a first software communication stack of a user equipment(UE), wherein the first software communication stack uses a firstsubscriber identity module (SIM) of the UE; receive a radio resourcecontrol (RRC) connection suspend request from the first softwarecommunication stack of the UE, wherein the RRC connection suspendrequest comprises information specifying a cause of the suspend requestas being a higher priority cellular communication of a second softwarecommunication stack using a second SIM of the UE; and store a connectionstate of the RRC connection of the first software communication stack ofthe UE, wherein the stored connection state is usable to restore the RRCconnection at a later time.

In some embodiments, the cellular network device may be furtherconfigured to: receive an RRC resume request from the first softwarecommunication stack of the UE, wherein the RRC resume request isreceived a period of time after receiving the RRC connection suspendrequest; and restore the stored connection state of the RRC connectionwith the first software communication stack of the UE.

In some embodiments, the cellular network device may be furtherconfigured to discontinue transfer of downlink data to the UE inresponse to receiving the RRC connection suspend request.

In other embodiments, a cellular network entity may comprise a radio,comprising one or more antennas for performing wireless communication;and a processing element operatively coupled to the radio; wherein thecellular network entity is configured to: establish a first radioresource control (RRC) connection with a first subscriber identitymodule (SIM) of a user equipment device (UE), wherein the first RRCconnection is in an inactive mode; receive a first notification from asecond cellular network entity to suspend the first RRC connection; inresponse to receiving the first notification, suspend the first RRCconnection and initiate a guard timer; receive a second indication fromthe second cellular network entity to resume the first RRC connection;transmit a preferred state indicator to the second cellular networkentity indicating a preferred state for resuming the first RRCconnection; and resume the first RRC connection with the first SIM ofthe UE according to the preferred state.

In some embodiments, the cellular network may operate such that thesecond indication is received after expiration of the timer, and thepreferred state indicator indicates a preference for an RRC idle state.

In some embodiments, the cellular network may operate such that thesecond indication is received before expiration of the timer, and thepreferred state indicator indicates a preference for either an RRCinactive state or an RRC connected state.

In some embodiments, a wireless user equipment (UE) device comprises aradio, comprising one or more antennas for performing wirelesscommunication, a processing element operatively coupled to the radio,and first and second subscriber identity modules (SIMs). Each of thefirst and second SIMs is coupled to the radio and configured to be usedwith the radio for wireless communication, wherein only one of the firstand second SIMs is used with the radio at any given time. The UE may beconfigured to perform cellular data communications with a first cellularnetwork using the first SIM and a first radio resource control (RRC)connection; and receive a request to perform a higher priority cellularcommunication with a second cellular network using the second SIM. Inresponse to the request to perform the higher priority cellularcommunication using the second SIM, the UE may suspend the first RRCconnection and may conduct the higher priority cellular communicationwith the second cellular network using the second SIM. When the higherpriority cellular communication is completed, the UE may send a releaseindication to the second network, and the UE may resume the first RRCconnection with the first SIM.

It is well understood that the use of personally identifiableinformation should follow privacy policies and practices that aregenerally recognized as meeting or exceeding industry or governmentalrequirements for maintaining the privacy of users. In particular,personally identifiable information data should be managed and handledso as to minimize risks of unintentional or unauthorized access or use,and the nature of authorized use should be clearly indicated to users.

Embodiments of the present disclosure may be realized in any of variousforms. For example, some embodiments may be realized as acomputer-implemented method, a computer-readable memory medium, or acomputer system. Other embodiments may be realized using one or morecustom-designed hardware devices such as ASICs. Still other embodimentsmay be realized using one or more programmable hardware elements such asFPGAs.

In some embodiments, a non-transitory computer-readable memory mediummay be configured so that it stores program instructions and/or data,where the program instructions, if executed by a computer system, causethe computer system to perform a method, e.g., any of a methodembodiments described herein, or, any combination of the methodembodiments described herein, or, any subset of any of the methodembodiments described herein, or, any combination of such subsets.

In some embodiments, a computer system may be configured to include aprocessor (or a set of processors) and a memory medium, where the memorymedium stores program instructions, where the processor is configured toread and execute the program instructions from the memory medium, wherethe program instructions are executable to implement any of the variousmethod embodiments described herein (or, any combination of the methodembodiments described herein, or, any subset of any of the methodembodiments described herein, or, any combination of such subsets). Thecomputer system may be realized in any of various forms. For example,the computer system may be a personal computer (in any of its variousrealizations), a workstation, a computer on a card, anapplication-specific computer in a box, a server computer, a clientcomputer, a hand-held device, a user equipment (UE), a tablet computer,a wearable computer, etc.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

We claim:
 1. A wireless user equipment (UE) device, the UE comprising: aradio, comprising one or more antennas for performing wirelesscommunication; a processing element operatively coupled to the radio;and first and second subscriber identity modules (SIMs), wherein each ofthe first and second SIMs is coupled to the radio and configured to beused with the radio for wireless communication, wherein only one of thefirst and second SIMs is used with the radio at any given time; whereinthe UE is configured to: perform cellular data communications with afirst cellular network using the first SIM and a first radio resourcecontrol (RRC) connection; and receive a request to perform a higherpriority cellular communication using the second SIM; in response to therequest to perform the higher priority cellular communication using thesecond SIM, transmit a request to the first cellular network to suspendthe first RRC connection; after transmission of the request to suspendthe first RRC connection, receive a message from the first cellularnetwork to place the first RRC connection in an inactive state; initiatea timer which measures an amount of time that the first RRC connectionis in the inactive state; wherein the measured amount of time is used todetermine whether the first RRC connection remains in the inactive stateor transitions to an idle state.
 2. The UE of claim 1, wherein the UE isfurther configured to: transition the first RRC connection from theinactive state to a connected state if the UE completes the higherpriority cellular communication using the second SIM prior to aspecified time duration.
 3. The UE of claim 2, wherein the UE isconfigured to transition the first RRC connection from the inactivestate to an idle state if the UE does not complete the higher prioritycellular communication using the second SIM prior to the specified timeduration.
 4. The UE of claim 3, wherein the message from the firstcellular network to place the first RRC connection in an inactive stateincludes the specified time duration.
 5. The UE of claim 1, wherein theUE further comprises: a first software communication stack whichperforms cellular communication using the first SIM; a second softwarecommunication stack which performs cellular communication using thesecond SIM; wherein the first software communication stack suspendsoperation in response to the request to perform the higher prioritycellular communication using the second SIM.
 6. The UE of claim 5,wherein upon receipt of the request to perform the higher prioritycellular communication using the second SIM, the second softwarecommunication stack requests the first software communication stack tosuspend operation; wherein the first software communication stacktransmits the request to the first cellular network to suspend the firstRRC connection in response to the request from the second softwarecommunication stack to suspend operation.
 7. The UE of claim 1, whereinthe request to the first cellular network to suspend the first RRCconnection comprises information specifying a cause of the suspendrequest being a higher priority cellular communication on a differentSIM.
 8. The UE of claim 1, wherein the information specifying the causeof the suspend request is used to maintain RRC state synchronizationbetween the first cellular network and the UE.
 9. The UE of claim 1,wherein the UE is further configured to: receive, by the first SIM, aresume request from the second SIM prior to expiration of the timer,wherein the resume request indicates that the first SIM may resume thefirst RRC connection; in response to the first SIM receiving the resumerequest, transmitting an RRC resume request to the first cellularnetwork, wherein the RRC resume request indicates a preferred RRC state;and resuming the first RRC connection according to the preferred RRCstate.
 10. A cellular network device, comprising: a processing element;a memory coupled to the processing element; wherein the cellular networkdevice is configured to: establish a first radio resource control (RRC)connection with a first software communication stack of a user equipment(UE), wherein the first software communication stack uses a firstsubscriber identity module (SIM) of the UE; receive a radio resourcecontrol (RRC) connection suspend request from the first softwarecommunication stack of the UE, wherein the RRC connection suspendrequest comprises information specifying a cause of the suspend requestas being a higher priority cellular communication of a second softwarecommunication stack using a second SIM of the UE; transmitting a messageto the first software communication stack of the UE specifying that thefirst RRC connection should be suspended, wherein the information alsospecifies that the first software communication stack should be placedin an inactive state.
 11. The cellular network device of claim 10,wherein the message further comprises a time duration during which thecellular network device considers the first software communication stackto be in an inactive state.
 12. The cellular network device of claim 11,wherein the time duration in the message specifies an amount of time inwhich the first software communication stack should be in an inactivestate before transitioning to an idle state.
 13. The cellular networkdevice of claim 11, wherein the cellular network device is furtherconfigured to: initiate a timer to measure an amount of time that thefirst RRC connection is suspended, wherein the timer is initiated inresponse to receiving the RRC connection suspend request; wherein if thecellular network receives a connection resume request from the firstsoftware communication stack of the UE prior to the timer counting tothe time duration, the cellular network is configured to instruct thefirst software communication stack of the UE to resume the first RRCconnection.
 14. The cellular network device of claim 13, wherein if thecellular network does not receive a connection resume request from thefirst software communication stack of the UE prior to the timer countingto the time duration, the cellular network is configured to mark thefirst software communication stack of the UE as being in an idle state.15. The cellular network device of claim 10, wherein the cellularnetwork device is further configured to: after transmitting the messageto the first software communication stack of the UE specifying that thefirst RRC connection should be suspended, transmitting paginginformation to the first software communication stack using a downlinknotification.
 16. The cellular network device of claim 10, whereinreceipt of the suspend request specifying the cause of the suspendrequest enables the cellular network device to maintain RRC statesynchronization with the first software communication stack of the UE.17. A non-transitory computer accessible memory medium for operating awireless user equipment (UE) device, wherein the memory medium stores: afirst software communication stack which operates with a firstsubscriber identity module (SIM) of the UE to perform wirelesscommunication using a single radio of the UE; a second softwarecommunication stack which operates with a second subscriber identitymodule (SIM) of the UE to perform wireless communication using thesingle radio of the UE; wherein the first software communication stackis configured to: perform cellular data communications with a firstcellular network using the first SIM and a first radio resource control(RRC) connection; and in response to a notification that the secondsoftware communication stack will be performing a higher prioritycellular communication using the second SIM, transmit a request to thefirst cellular network to suspend the first RRC connection; in responseto the request to suspend the first RRC connection, receive a messagefrom the first cellular network instructing the first softwarecommunication stack to be placed in an inactive mode, wherein themessage includes a specified time duration; initiating a timer whichmeasures an amount of time that the first RRC connection is suspended;transition the first RRC connection from the inactive state to aconnected state if the UE completes the higher priority cellularcommunication using the second SIM prior to the specified time duration.18. The non-transitory computer accessible memory medium of claim 17,wherein the first software communication stack is further configured totransition the first RRC connection from the inactive state to an idlestate if the second software communication stack does not complete thehigher priority cellular communication using the second SIM prior to thespecified time duration.
 19. The non-transitory computer accessiblememory medium of claim 18, wherein the request to the first cellularnetwork to suspend the first RRC connection comprises informationspecifying a cause of the suspend request being a higher prioritycellular communication on a different SIM.
 20. The non-transitorycomputer accessible memory medium of claim 19, wherein the informationspecifying the cause of the suspend request is used to maintain RRCstate synchronization between the first cellular network and the UE.